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<head><meta charset="utf-8"><title>I-prioritize #78234 unreachable pattern not warned when use… · t-compiler/wg-prioritization/alerts · Zulip Chat Archive</title></head>
<h2>Stream: <a href="https://rust-lang.github.io/zulip_archive/stream/245100-t-compiler/wg-prioritization/alerts/index.html">t-compiler/wg-prioritization/alerts</a></h2>
<h3>Topic: <a href="https://rust-lang.github.io/zulip_archive/stream/245100-t-compiler/wg-prioritization/alerts/topic/I-prioritize.20.2378234.20unreachable.20pattern.20not.20warned.20when.20use.E2.80.A6.html">I-prioritize #78234 unreachable pattern not warned when use…</a></h3>

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<a name="214197511"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/245100-t-compiler/wg-prioritization/alerts/topic/I-prioritize%20%2378234%20unreachable%20pattern%20not%20warned%20when%20use%E2%80%A6/near/214197511" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> triagebot <a href="https://rust-lang.github.io/zulip_archive/stream/245100-t-compiler/wg-prioritization/alerts/topic/I-prioritize.20.2378234.20unreachable.20pattern.20not.20warned.20when.20use.E2.80.A6.html#214197511">(Oct 22 2020 at 14:46)</a>:</h4>
<p><span class="user-group-mention" data-user-group-id="3111">@WG-prioritization/alerts</span> issue <a href="https://github.com/rust-lang/rust/issues/78234">#78234</a> has been requested for prioritization.</p>
<h1><a href="https://forge.rust-lang.org/compiler/prioritization/procedure.html#assign-priority-to-unprioritized-issues-with-i-prioritize-label">Procedure</a></h1>
<ul>
<li>Priority?</li>
<li>Regression?</li>
<li>Notify people/groups?</li>
<li>Needs <code>I-nominated</code>?</li>
</ul>



<a name="214198052"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/245100-t-compiler/wg-prioritization/alerts/topic/I-prioritize%20%2378234%20unreachable%20pattern%20not%20warned%20when%20use%E2%80%A6/near/214198052" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Hameer Abbasi <a href="https://rust-lang.github.io/zulip_archive/stream/245100-t-compiler/wg-prioritization/alerts/topic/I-prioritize.20.2378234.20unreachable.20pattern.20not.20warned.20when.20use.E2.80.A6.html#214198052">(Oct 22 2020 at 14:49)</a>:</h4>
<p>Does Rust have a guarantee that the first matching arm will be hit, and not any other? Or could any of the matching arms be hit?</p>
<p>If it does have this guarantee, this is pretty bad, possibly unsound.</p>



<a name="214198609"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/245100-t-compiler/wg-prioritization/alerts/topic/I-prioritize%20%2378234%20unreachable%20pattern%20not%20warned%20when%20use%E2%80%A6/near/214198609" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Joshua Nelson <a href="https://rust-lang.github.io/zulip_archive/stream/245100-t-compiler/wg-prioritization/alerts/topic/I-prioritize.20.2378234.20unreachable.20pattern.20not.20warned.20when.20use.E2.80.A6.html#214198609">(Oct 22 2020 at 14:53)</a>:</h4>
<p>it guarentees the first matching arm will be hit</p>



<a name="214198615"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/245100-t-compiler/wg-prioritization/alerts/topic/I-prioritize%20%2378234%20unreachable%20pattern%20not%20warned%20when%20use%E2%80%A6/near/214198615" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Joshua Nelson <a href="https://rust-lang.github.io/zulip_archive/stream/245100-t-compiler/wg-prioritization/alerts/topic/I-prioritize.20.2378234.20unreachable.20pattern.20not.20warned.20when.20use.E2.80.A6.html#214198615">(Oct 22 2020 at 14:53)</a>:</h4>
<p>this is just a lint</p>



<a name="214204332"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/245100-t-compiler/wg-prioritization/alerts/topic/I-prioritize%20%2378234%20unreachable%20pattern%20not%20warned%20when%20use%E2%80%A6/near/214204332" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Hameer Abbasi <a href="https://rust-lang.github.io/zulip_archive/stream/245100-t-compiler/wg-prioritization/alerts/topic/I-prioritize.20.2378234.20unreachable.20pattern.20not.20warned.20when.20use.E2.80.A6.html#214204332">(Oct 22 2020 at 15:33)</a>:</h4>
<p>Ah, I read the panic too quickly and thought it was for the <code>unreachable!</code> arm rather than the <code>assert!</code>.</p>



<a name="214217083"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/245100-t-compiler/wg-prioritization/alerts/topic/I-prioritize%20%2378234%20unreachable%20pattern%20not%20warned%20when%20use%E2%80%A6/near/214217083" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> Noah Lev <a href="https://rust-lang.github.io/zulip_archive/stream/245100-t-compiler/wg-prioritization/alerts/topic/I-prioritize.20.2378234.20unreachable.20pattern.20not.20warned.20when.20use.E2.80.A6.html#214217083">(Oct 22 2020 at 17:05)</a>:</h4>
<p>Seems like P-medium or even P-low to me - probably something hard to fix and not a huge deal since it's just a warn-by-default lint. But of course would be good to fix :)</p>



<a name="214818656"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/245100-t-compiler/wg-prioritization/alerts/topic/I-prioritize%20%2378234%20unreachable%20pattern%20not%20warned%20when%20use%E2%80%A6/near/214818656" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> apiraino <a href="https://rust-lang.github.io/zulip_archive/stream/245100-t-compiler/wg-prioritization/alerts/topic/I-prioritize.20.2378234.20unreachable.20pattern.20not.20warned.20when.20use.E2.80.A6.html#214818656">(Oct 28 2020 at 10:38)</a>:</h4>
<p>I'll set <code>P-low</code> after <span class="user-mention silent" data-user-id="125294">Aaron Hill</span> comment, there is a patch coming up for procedural macros.  But ok to tick that as P-medium if it suits better.</p>



<a name="214818693"></a>
<h4><a href="https://rust-lang.zulipchat.com#narrow/stream/245100-t-compiler/wg-prioritization/alerts/topic/I-prioritize%20%2378234%20unreachable%20pattern%20not%20warned%20when%20use%E2%80%A6/near/214818693" class="zl"><img src="https://rust-lang.github.io/zulip_archive/assets/img/zulip.svg" alt="view this post on Zulip" style="width:20px;height:20px;"></a> triagebot <a href="https://rust-lang.github.io/zulip_archive/stream/245100-t-compiler/wg-prioritization/alerts/topic/I-prioritize.20.2378234.20unreachable.20pattern.20not.20warned.20when.20use.E2.80.A6.html#214818693">(Oct 28 2020 at 10:39)</a>:</h4>
<p>Issue <a href="https://github.com/rust-lang/rust/issues/78234">#78234</a>'s prioritization request has been removed.</p>



<hr><p>Last updated: Aug 07 2021 at 22:04 UTC</p>
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